The present invention relates generally to police radar detectors used in motor vehicles and, more particularly, to a police radar detector which not only detects the presence of radar signals incident on a motor vehicle but also determines the direction of the source of the radar signals and alerts the operator of the motor vehicle of both radar signal presence and source direction.
Radar signals have been commonly used by police for some time to determine the speed of motor vehicles. In response to radar speed monitoring and to signal motor vehicle operators when such monitoring is taking place, police radar detectors have likewise been used for almost a coincident period of time. Currently available radar detectors indicate the presence of radar signals, the frequency band of detected signals and the relative field strength of detected signals. The widely varying operating procedures for using police radar and the proliferation of other signals assigned to the same frequency bands as police radar has led to the need for police radar detectors which give more information than that provided by current radar detectors.
For example, police radar units are often deployed along the side of the roadway, to measure a motor vehicle's speed as it advances toward the unit. In some instances, the police radar may measure the speed of a motor vehicle after it has passed and is travelling away from the unit. Police vehicles may also be equipped with radar units which are operated while the police vehicles are moving, using reflections from stationary objects to measure the speed of the police vehicle itself, and reflections from a target vehicle to measure relative speed, and using both measured speeds to determine the actual speed of the target vehicle.
When a vehicle equipped with a radar detector is within microwave range of a police radar unit which transmits a radar signal, the detector alerts the vehicle operator that the signal is present typically through a combination of audible and visual signals. As the user approaches the source of the radar signal, signal strength normally indicated by the typical detector increases. As the vehicle passes the source of the radar signal, the indicated signal strength drops, usually very quickly, since a forwardly aimed directional antenna of the detector is no longer pointed in the general direction of the signal source, and is now responding to reflections of the signal from objects in front of the vehicle. If the police radar unit is at the side of the road in a clearly visible location, the vehicle operator can easily correlate the detected signal and its apparent source.
If, on the other hand, the police radar unit is not visible, for example because it is in an unmarked car, it is dark, or the radar signal source is actually on a different nearby roadway not visible to the vehicle operator, the source of the radar signal cannot readily be determined. Further, under such conditions, when the detector indicates a drop in signal strength apparently indicating that the vehicle has passed a radar source, the vehicle operator cannot be sure whether the source is now behind the vehicle or if the drop in signal strength is due to terrain changes caused by movement of the vehicle.
In addition to the possible variations in police radar signal encounters, there are many different sources of microwave signals in the frequency bands allocated to police radar by the U.S. Federal Communications Commission (FCC) since these bands have also been allocated for transmitters performing other functions. For example, motion-detecting burglar alarms, automatic door openers, and low-power speed measuring devices used in sports also operate in the frequency bands allocated to police radar. Unfortunately, police radar detectors cannot distinguish between signals generated by a police radar transmitter and those generated by other devices which utilize microwave signals within the same frequency bands. The inability to distinguish these signals is a disadvantage of police radar detectors, particularly in urban areas where the number of non-police microwave signals may be relatively high.
Accordingly, there is a need for an improved police radar detector which can assist the operator of a motor vehicle using the detector to accurately interpret signals generated by the detector to alert the operator of police radar signals incident on the motor vehicle.